Bind source address for cluster communication

The first address specified as a bind parameter
(server.bindaddr[0]) gets used as the source IP
for cluster communication.

If no bind address is specified by the user, the
behavior is unchanged.

This patch allows multiple Redis Cluster instances
to communicate when running on the same interface
of the same host.

src/anet.c

@@ -234,11 +234,12 @@ static int anetCreateSocket(char *err, int domain) {
 
 #define ANET_CONNECT_NONE 0
 #define ANET_CONNECT_NONBLOCK 1
-static int anetTcpGenericConnect(char *err, char *addr, int port, int flags)
+static int anetTcpGenericConnect(char *err, char *addr, int port,
+                                 char *source_addr, int flags)
 {
     int s = ANET_ERR, rv;
     char portstr[6];  /* strlen("65535") + 1; */
-    struct addrinfo hints, *servinfo, *p;
+    struct addrinfo hints, *servinfo, *bservinfo, *p, *b;
 
     snprintf(portstr,sizeof(portstr),"%d",port);
     memset(&hints,0,sizeof(hints));
@@ -258,6 +259,24 @@ static int anetTcpGenericConnect(char *err, char *addr, int port, int flags)
         if (anetSetReuseAddr(err,s) == ANET_ERR) goto error;
         if (flags & ANET_CONNECT_NONBLOCK && anetNonBlock(err,s) != ANET_OK)
             goto error;
+        if (source_addr) {
+            int bound = 0;
+            /* Using getaddrinfo saves us from self-determining IPv4 vs IPv6 */
+            if ((rv = getaddrinfo(source_addr, NULL, &hints, &bservinfo)) != 0) {
+                anetSetError(err, "%s", gai_strerror(rv));
+                goto end;
+            }
+            for (b = bservinfo; b != NULL; b = b->ai_next) {
+                if (bind(s,b->ai_addr,b->ai_addrlen) != -1) {
+                    bound = 1;
+                    break;
+                }
+            }
+            if (!bound) {
+                anetSetError(err, "bind: %s", strerror(errno));
+                goto end;
+            }
+        }
         if (connect(s,p->ai_addr,p->ai_addrlen) == -1) {
             /* If the socket is non-blocking, it is ok for connect() to
              * return an EINPROGRESS error here. */
@@ -287,12 +306,17 @@ end:
 
 int anetTcpConnect(char *err, char *addr, int port)
 {
-    return anetTcpGenericConnect(err,addr,port,ANET_CONNECT_NONE);
+    return anetTcpGenericConnect(err,addr,port,NULL,ANET_CONNECT_NONE);
 }
 
 int anetTcpNonBlockConnect(char *err, char *addr, int port)
 {
-    return anetTcpGenericConnect(err,addr,port,ANET_CONNECT_NONBLOCK);
+    return anetTcpGenericConnect(err,addr,port,NULL,ANET_CONNECT_NONBLOCK);
+}
+
+int anetTcpNonBlockBindConnect(char *err, char *addr, int port, char *source_addr)
+{
+    return anetTcpGenericConnect(err,addr,port,source_addr,ANET_CONNECT_NONBLOCK);
 }
 
 int anetUnixGenericConnect(char *err, char *path, int flags)

src/anet.h

@@ -45,6 +45,7 @@
 
 int anetTcpConnect(char *err, char *addr, int port);
 int anetTcpNonBlockConnect(char *err, char *addr, int port);
+int anetTcpNonBlockBindConnect(char *err, char *addr, int port, char *source_addr);
 int anetUnixConnect(char *err, char *path);
 int anetUnixNonBlockConnect(char *err, char *path);
 int anetRead(int fd, char *buf, int count);

src/cluster.c

@@ -2424,9 +2424,14 @@ void clusterCron(void) {
             mstime_t old_ping_sent;
             clusterLink *link;
 
-            fd = anetTcpNonBlockConnect(server.neterr, node->ip,
-                node->port+REDIS_CLUSTER_PORT_INCR);
-            if (fd == -1) continue;
+            fd = anetTcpNonBlockBindConnect(server.neterr, node->ip,
+                node->port+REDIS_CLUSTER_PORT_INCR, server.bindaddr[0]);
+            if (fd == -1) {
+                redisLog(REDIS_DEBUG, "Unable to connect to "
+                    "Cluster Client [%s]:%d", node->ip,
+                    node->port+REDIS_CLUSTER_PORT_INCR);
+                continue;
+            }
             link = createClusterLink(node);
             link->fd = fd;
             node->link = link;